In motor control applications, knowledge of the motor temperature is often desired for current scheduling and/or overload protection. Generally, there are two methods of obtaining a temperature indication: actual measurement, and estimation.
The first method, actual measurement, is carried out with a temperature responsive device such as a thermistor. The device is typically mounted inside the housing of the motor and thereby provides a reliable and relatively accurate indication of the temperature. However, this approach significantly increases the cost of the installation since an additional dedicated conductor pair is required to connect the sensing device to the motor controller. The use of an additional dedicated conductor pair also requires an additional motor controller port and larger connectors.
The second method, estimation, is based on a theoretical or empirically derived model of the motor, and typically requires knowledge of the motor current, the ambient temperature and heat dissipation capacity of the motor. The approach does not significantly affect the cost of the installation, but the resulting temperature indication is only as reliable and accurate as the model.